In gas turbine engines, fuel is burned within a combustion chamber to produce hot gases of combustion. The gases are expanded within a turbine section producing a gas stream across alternating rows of stationary stator vanes and turbine rotor blades, attached to a turbine wheel, to produce usable power. Gas stream temperatures at the initial rows of vanes and blades commonly exceed 2,000 degrees Fahrenheit. Blades and vanes, susceptible to damage by the hot gas stream, are cooled by air compressed upstream within the engine and flowed to the turbine components. One method for cooling rotating turbine wheels includes injecting cooling air from stationary cavities within the engine to a cooling slot within the turbine wheel for distribution to the interior of the turbine blades.
Air cooling is sometimes not sufficient to prevent low cycle fatigue due to the presence of stress concentrations in the turbine wheel. Overall efficiency in the operation of turbines can be improved by the removal of stress concentrations, thereby reducing stress related damage and in turn reducing downtime of the turbine. The art would be further benefited by the removal of stress concentrations while the turbine wheel is mounted in a turbine.
Prior to the present invention, the utility operator who desired to modify the cooling slots to reduce stress concentrations had essentially two choices: first, the entire rotor could be replaced and, secondly, the turbine wheel could be removed from the turbine to be modified.
Accordingly, a method and apparatus that would allow modification of a turbine wheel cooling slot to remove or reduce stress concentrations, and particularly, a method and apparatus for in-situ modification is desired.